The present invention generally relates to electrical robots, and more particularly to an electrical robot which carries out a predetermined operation when rotational driving forces of motors are transmitted thereto.
Generally, an articulated electrical robot for carrying out an operation such as a painting operation and a welding operation comprises a rotary base, a support beam, an arm, a wrist mechanism and the like. Each movable part of the electrical robot is driven by a rotational driving force of a motor, so that the electrical robot plays back a programmed operation.
One example of the conventional electrical robot of this type is disclosed in a Japanese Published Patent Application No. 61-12140. According to this conventional electrical robot, a motor for driving the support beam which is provided on the rotary base and is free to turn up and down, a motor for driving the arm which is supported on an upper end of the support beam, motors for driving the wrist mechanism which is mounted on a tip end of the arm and the like are respectively provided at low positions of the support beam in vicinities of the rotary base. In addition, each motor projects in a horizontal direction from the low position of the support beam. The motors for driving the wrist mechanism in particular are mounted on the rear of the other motors for driving the arm and the support beam.
Generally, various obstacles such as apparatuses are provided in the surroundings of a production line where the electrical robot is located, and an operation region in which the electrical robot can operate is often limited. However, since the motors project in the horizontal direction from the low positions in the vicinities of the rotary base, the motors, especially the motors which are provided on the rear of the other motors for driving the wrist mechanism, may move out of the operation region and hit the obstacles in the surroundings when the arm is turned by rotating the rotary base.
In order to prevent the motors for driving the wrist mechanism from hitting the obstacles in the surroundings, it is possible to conceive such an arrangement that these motors are mounted on a base portion of the arm. When the motors for driving the wrist mechanism are mounted on the arm, it is possible to prevent the motors from hitting the obstacles in the surroundings because the mounting positions of the motors become high. However, there are problems in that the weight of the arm increases and it becomes necessary to employ a large motor having a sufficient power to drive the arm. As a result, the operation characteristic of the arm becomes poor.
On the other hand, since each motor is provided at the low position of the support beam in order to prevent the operation characteristic of each part of the electrical robot from becoming deteriorated due to inertia of each part when it moves, a transmitting path between each motor and a corresponding part of the electrical robot driven thereby is relatively long. For this reason, there is also a problem in that the construction of particularly a transmitting mechanism for transmitting the rotational driving force of the motor for driving the wrist mechanism to the wrist mechanism becomes complex due to the relatively long transmitting path therebetween.
In addition, it is desirable that the motor part is located at such a position that the maintenance thereof is easy to carry out.